Oral Presentation

The Earth's materials deform intensely at plate boundaries and are constantly worked at the surface by urbanization, changing shallow hydrology, and dynamic landscapes. This talk will review the evidence from long-term observations that temporal changes in seismic properties, both near faults and near sites, are detectable in the continuous recordings of seismograms. 20+ years of continuous data in the state of California contain not only earthquake signals and tectonic tremors but also ambient seismic fields that carry the seismic signature of Earth materials. The continuous data now spans the time scale of earthquake cycles, such as Parkfield, and a changing climate and hydrosphere. Near faults, these seismic properties mark the signature of interseismic tectonic loading, shaking-induced damage, and healing of fault materials. Near the surface, the seismic properties, the most significant contributors to high-frequency ground motions, are constantly modulated by variable stress conditions due to periodic air temperature conditions and the load and diffusion of highly variable, or absent, rainfall. Monitoring the change of the subsurface complements well the satellite measurements of surface deformation, which, together, can deliver a novel picture of Geodynamics.